A strontium isotope and trace element profile through the Partridge River Troctolite,Duluth complex,Minnesota     

Norman K. Grant  Philip A. Molling 《Contributions to Mineralogy and Petrology》1981,77(3):296-305

Initial ⁸⁷Sr/⁸⁶Sr ratios down a 2,315 foot-long core (DDH-295) through the Partridge River Troctolite are lower in the depth range 710–1,410 feet (0.70443±22) than in the underlying and overlying rocks (0.70500±18). These initial ratio variations define three zones (I, II, and III) thought to be three intrusive units within the troctolite. The best estimate of the Rb-Sr age of the troctolite is 1,050±105 m.y. The olivine compositions and the abundances of the incompatible trace elements Zr, Y, and Rb show identical variations down the core, with downward repetitions of olivine iron-enrichment and incompatible trace element enrichments. Discontinuities in the olivine compositions and incompatible trace element abundances match the initial ⁸⁷Sr/⁸⁶Sr ratio discontinuities in the core. The strontium isotope data imply that involatile components of the Proterozoic Virginia Formation and other Archaean rocks were not significantly assimilated by the troctolites, for only three out of the twenty-three initial ⁸⁷Sr/⁸⁶Sr ratios depart from normal magmatic values. These three anomalous ratios are not systematically related to the Cu-Ni sulphide mineralization and may be the result of secondary calcite in the troctolite. The strontium isotope systematics of the Virginia Formation xenoliths and underlying hornfelses are highly disturbed as a result of Rb loss. The apparently inverted fractionation sequences in the troctolites are interpreted in terms of downward increases in intercumulus liquid in repeated magma batches and controlled by plagioclase flotation. The amount of intercumulus liquid is estimated to range from 7 to 61 weight per cent. The Cu-Ni sulphides are concentrated in the lower 250 feet of zone I (immediately above the Virginia Formation) and through 400 feet of core across the contact between zones I and II, more than 750 feet above the base. Because the sulphide-bearing troctolites are not systematically related to disturbances in the magmatic initial ⁸⁷Sr/⁸⁶Sr ratios, the mineralization probably involved the volatile transfer of sulphur derived from dehydration reactions in the underlying Virginia Formation.  相似文献   

Acid Mining Lakes     

Norman D. Yan 《Journal of Paleolimnology》2001,26(1):109-111

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Discussion of: Nelson, C.E., 2000, Volcanic domes and gold mineralization in the Pueblo Viejo district, Dominican Republic. Mineralium Deposita, vol. 35, pp. 511-525     

Stephen E. Kesler  Norman Russell 《Mineralium Deposita》2001,36(5):465-468

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A plea to subdivide the Chalk on future maps in a manner applicable tothe whole of Britain     

Norman B. Peake 《Proceedings of the Geologists' Association. Geologists' Association》2002,113(4):345-347

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Display and processing of seismic wide angle reflection data from expendable sonobuoys     

J. J. Langford  P. R. Miles 《Marine Geophysical Researches》1978,3(4):413-420

A method for the display of expendable sonobuoy data using a variable area recorder has been developed to improve the effectiveness and interpretation of the data. Each signal trace is digitised, processed and delayed using a mini-computer capable of shipboard operation. The final display flattens the reflection hyperbolae and enables improved trace correlation and reflector digitisation. The method has particular application to the interpretation of poor quality records.  相似文献   

Sulfate reduction in deep coastal marine sediments   总被引：1，自引：0，他引：1  

Harry M Edenborn  Norman Silverberg  Alfonso Mucci  Bjrn Sundby 《Marine Chemistry》1987,21(4)

Sulfate reduction rates in sediments of four deep stations in the Saguenay Fjord and the Laurentian Trough, Gulf of St. Lawrence, are among the lowest reported for the coastal environment. Maximum rates were 0.4–7.0 nmol cm⁻³ day⁻¹. The low rates are due to relatively low sedimentation rates and continuously low temperatures. Regional differences in both integrated and maximum sulfate reduction rates in the sediment correlate with sediment trap measurements of sedimentation rate and organic carbon flux.Sulfate reduction accounts for the degradation of 5–26% of the estimated downward flux of organic matter to these sediments. Unlike the absolute rate of sulfate reduction, the relative proportion of the carbon flux that is degraded via sulfate reduction is not directly correlated with the sedimentation rate but is a function of organic matter composition, intensity of bioturbation, and the abundance of sub-oxic electron acceptors. Thus, the lowest proportion of carbon degradation via sulfate reduction occurred at a Gulf site, where a combination of low sedimentation and bioturbation rates allowed a long residence time for organic matter near the sediment surface and, in consequence, a low flux of labile carbon into the sulfate reduction zone. The highest proportion was observed at a station with a similar organic carbon flux but with higher rates of sedimentation and bioturbation. At a third site, with the highest rates of sulfate reduction as well as the highest rates of sedimentation and bioturbation, the contribution of sulfate reduction to organic matter degradation was only intermediate. This is attributable to the exhaustion of the supply of porewater sulfate. In deep coastal environments the proportion of organic matter degraded via sulfate reduction can be highly variable both spatially and temporally.  相似文献   

Fishing practice, gear design, and the ecosystem approach three case studies demonstrating the effect of management strategy on gear selectivity and discards     

Graham  Norman; Ferro  Richard S. T.; Karp  William A.; MacMullen  Philip 《ICES Journal of Marine Science》2007,64(4):744-750

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What is a wave-dominated coast?   总被引：10，自引：0，他引：10  

Richard A. Davis Jr.  Miles O. Hayes 《Marine Geology》1984,60(1-4):313-329

During the past decade or so, various coasts have been designated as wave-dominated or tide-dominated. Typically there is an association made between coastal morphology and the dominant process that operates on the coast in question. Most authors consider long, smooth, barrier coasts with few inlets and poorly developed ebb deltas as “wave-dominated”. These coasts are associated with microtidal ranges. Conversely, mesotidal coasts tend to develop short, drumstick-shaped barriers with well-developed ebb deltas. They are considered as tide-dominated barriers. Such generalizations may be restricted to coasts with moderate wave energy although this is commonly not stated.

Exceptions to these stated generalizations are so numerous that wave energy and tidal prism must also be included in characterizing coasts. The relative effects of waves and tides are of extreme importance. It is possible to have wave-dominated coasts with virtually any tidal range and it is likewise possible to have tide-dominated coasts even with very small ranges. The overprint of tidal prism will also produce tide-dominated morphology on coasts with microtidal ranges.  相似文献   

Thermal migration of water on the Galilean satellites     

Norman G. Purves  Carl B. Pilcher 《Icarus》1980,43(1):51-55

We have modeled the thermal migration of water on the Galilean satellites under the assumption of ballistic molecular trajectories. We find that water migrating owing to solar radiation on an ice-covered satellite will build up in the temperate latitudes, in general not reaching the poles. As much as 50 m of ice may have been lost by this process from the equatorial regions of Europa over the age of the solar system. The disappearance of patches of ice—for instance, the bright rays surrounding some impact craters—from the equatorial regions of Ganymede and Callisto may approach a value (the irreversible evaporation rate) three orders of magnitude larger than the net equatorial loss rate for ice-covered Europa. The presence of water ice pole caps on Ganymede extending to the latitudes at which thermal migration becomes important suggests that some process distributed an extensive, thin covering of water on the satellite, and that the equatorial regions were subsequently cleared by the thermal process.  相似文献   

Luna 24 ferrobasalt as a low-Mg primary melt     

Marc Norman  Graham Ryder 《Earth, Moon, and Planets》1980,23(3):271-292

Luna 24 very-low titanium (VLT) ferrobasalts, metabasalts, brown glasses and impact melts form a tight compositional cluster with no gradation to other groupings postulated for the Luna 24 core components. This suggests that the Luna 24 VLT ferrobasalt was extruded as a liquid of its own composition and was not derived by fractional crystallization from a more magnesian parent in a surface flow. Furthermore, the characteristics of the core lithologies are not easily visualized as components of such a differentiated flow, e.g. brown glasses. Gravitative settling models purporting to demonstrate the validity of the flow differentiation model are merely permissive.Subsurface fractionation requires that plagioclase, not olivine, be the liquidus phase.The high-Mg component in the Luna 24 core can be constrained, though not identified, chemically, and it has neither the major element, trace element, isotopic, nor mineralogical characteristics required of a possible parent to the Luna 24 VLT ferrobasalt. Thus models of fractionation lack a physical expression of the less differentiated compositions, contrary to the belief that the high-Mg component in the core is the parent material.The Luna 24 VLT ferrobasalt is probably a primary low-Mg melt from a plagioclase-bearing source region, and may have undergone little or no fractionation prior to eruption. Such a model is compatible with, and suggested by, chemical and experimental data. Caution against postulating that all Mg-poor melts are fractionated products, based on terrestrial models, is advised. The terrestrial oceanic situation of primary melts with similar Mg/Fe is probably not valid for the Moon.  相似文献